Structurally robust and pH-responsive Pickering emulsions enabled by interfacial biopolymer networks for active and intelligent packaging.

Abstract

pH-responsive Pickering emulsions were promising for controlled release, yet smart responsiveness and interfacial stability remain fundamentally at odds. Herein, a pH-responsive and structurally robust composite Pickering emulsion, denoted as STTCx (SPI-TTO-TA-CSx), was fabricated using soy protein isolate (SPI), tea tree oil (TTO), tannic acid (TA), and chitosan (CS). Oxidized tannic acid (OTA) reacted with SPI via Schiff-base chemistry to generate SPI-OTA complexes containing acid-labile imine bonds (C=N), as evidenced by macroscopic observations before and after oxidation and further supported by FTIR analysis, which served as interfacial particles to stabilize TTO droplets with an SPI-OTA shell. Subsequent electrostatic deposition of chitosan formed a dense outer layer, markedly enhancing interfacial robustness. The emulsions remained stable for at least 21 days at room temperature. Incorporation of STTCx into a chitosan matrix yielded an active film with high TTO encapsulation efficiency (83.4%), strong antioxidant capacity (96.27% DPPH scavenging and 81.63% ABTS scavenging), and acid-triggered release. It could effectively extend the shelf life of pork by more than 7 days during refrigerated storage at 4 °C.